Page:Smithsonian Miscellaneous Collections, Volume 85.djvu/631

 Roeblino Fund

THE DETERMINATION OF OZONE BY SPECTROBOLOMETRIC MEASUREMENTS By OLIVER R. WULF Smithsonian Institution and U. S. Bureau of Chemistry and Soils

(With Three Plates)

In the fall of 1930, at the suggestion of Dr. C. G. Abbot, measure- ments of the transmission of visible light by ozone were made on the solar spectrometer of the Smithsonian Institution at Table IMountain. Calif. This determination of the absorption of ozone in the region of its very weak absorption, practical in the laboratory only by the method of photographic photometry, by which it has been done by Colange/ can be accomplished by direct energy measurements on the spectrobolometer because of its great sensitiveness and the extreme intensity of the source. At the same time fluctuations in weather conditions are likewise registered with great sensitiveness and consti- tute a serious source of error in the measurements. But on the other hand it is favorable that observations may be made of the absorption of controlled amounts of ozone placed in the sun's beam with all other conditions of operation identical with those of the regular solar observations. One of the useful results of this work has been the selecting of a large number of points on the solar hologram which may be satisfactorily used for ozone determination. The present paper has to do for the most part with the results of these measurements as forming a basis for the determination of atmospheric ozone from solar holograms and not with the results of their application.

The essential apparatus used in this work auxiliary to the spec- trometer is shown in Plate i. A cylindrical glass cell, 20.0 cm. long and approximately 13 cm. in diameter, was mounted in the front room of the spectrometer tunnel in such a way that it could be easily moved in or out of the solar beam as it came from the coelostat mir- rors on its way to the first slit of the instrument. The circular windows of this cell were made of high-grade plane plate glass. These windows ^ Colange, G., Journ. Phys. et le Rad., ser. 6, vol. 8, p. 254, 1927.

Smithsonian Miscellaneous Collections, Vol.85, No. 9